99 lines
2.6 KiB
Markdown
99 lines
2.6 KiB
Markdown
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---
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id: 5a24c314108439a4d403617c
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challengeType: 6
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forumTopicId: 301423
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localeTitle: 使用生命周期方法:componentWillMount
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---
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## Description
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<section id='description'>
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React 组件有几种特殊方法,可以在组件生命周期的特定点执行操作。这些称为生命周期方法或生命周期钩子,允许你在特定时间点捕获组件。这可以在渲染之前、更新之前、接收 props 之前、卸载之前等等。以下是一些主要生命周期方法的列表:
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<code>componentWillMount()</code>
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<code>componentDidMount()</code>
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<code>shouldComponentUpdate()</code>
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<code>componentDidUpdate()</code>
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<code>componentWillUnmount()</code>
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接下来的几节课将讲述这些生命周期方法的一些基本用例。
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<strong>注意:</strong> `componentWillMount` 生命周期方法会在版本 16.X 废弃在版本 17 移除 [(Source)](https://reactjs.org/blog/2018/03/27/update-on-async-rendering.html)
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</section>
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## Instructions
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<section id='instructions'>
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当组件被挂载到 DOM 时,<code>componentWillMount()</code>方法在<code>render()</code>方法之前被调用。在<code>componentWillMount()</code>中将一些内容记录到控制台--你需要打开浏览器控制台以查看输出。
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>MyComponent</code>应该渲染一个<code>div</code>元素。
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testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); return mockedComponent.find('div').length === 1; })());
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- text: 应该在<code>componentWillMount</code>中调用<code>console.log</code>。
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testString: assert((function() { const lifecycle = React.createElement(MyComponent).type.prototype.componentWillMount.toString().replace(/ /g,''); return lifecycle.includes('console.log('); })());
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='jsx-seed'>
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```jsx
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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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}
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componentWillMount() {
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// change code below this line
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// change code above this line
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}
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render() {
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return <div />
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}
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};
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```
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</div>
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### After Test
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<div id='jsx-teardown'>
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```js
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ReactDOM.render(<MyComponent />, document.getElementById('root'))
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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}
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componentWillMount() {
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// change code below this line
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console.log('Component is mounting...');
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// change code above this line
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}
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render() {
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return <div />
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}
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};
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```
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</section>
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